The present invention relates to a head unit for a serial type ink jet printer to which ink is supplied from an ink tank, and more particularly to a head unit having a damper mechanism capable of reliably suppressing the fluctuation of ink pressure occurring due to the movement of the head unit. The present invention also relates to an ink jet printer incorporating such a head unit.
In a serial type ink jet printer having a construction in which an ink tank and a head unit mounted on a carriage are connected by a flexible ink tube, when the head unit is moved by the carriage, pressure is applied to the ink which is supplied to the head unit. This pressure is largely dependent on the acceleration of the head unit, the length of an ink passage from the ink tank to the head unit, and the specific weight of the ink. If this pressure is applied to a nozzle orifice of the head unit, it becomes impossible to properly discharge ink droplets, which can cause faulty printing such as the splashing of ink droplets, dot omission or the like.
Accordingly, the head unit is provided with a damper mechanism for absorbing the pressure applied to the ink passage in conjunction with the movement of the head unit. For example, Japanese Patent Publications Nos. 3-224744A and 4-269553A disclose head units having such damper mechanisms.
As disclosed in these publications, the related-art head unit is provided with a shape in which it is elongated in a direction perpendicular to the nozzle formation face. Namely, the related-art head unit is provided with a shape in which it is elongated in a direction perpendicular to the moving direction of the head unit. The reason for this is that it is considered that the damper effect can be obtained efficiently if a damping chamber is disposed in a direction perpendicular to the moving direction of the head unit.
However, the pressure which can be absorbed by the damper mechanism mounted in the head unit is the pressure acting in the ink passage between the damper mechanism and the ink tank, and the pressure acting in the ink passage from the damper mechanism to the nozzle orifice cannot be absorbed. Accordingly, in the case where the head unit is provided with the shape in which it is elongated in the direction perpendicular to the nozzle formation face as in the related art, the ink passage from the damper mechanism to the nozzle orifice becomes long, so that large pressure is produced in the ink passage in conjunction with the movement of the head unit, and is directly transmitted to the nozzle orifice. Hence, such drawbacks as the dot omission have been liable to occur.
In addition, the head unit having a shape in which it is elongated in the direction perpendicular to the moving direction requires much space for its movement, which has constituted a hindrance to the effort to make the ink jet printer compact.